Fetal heart rate (FHR) monitoring is now widely used during labor. The technique is based on the hypothesis that FHR patterns indicative of hypoxemia are identifiable. The "ominous" patterns have been correlated with poor fetal acidosis. Several studies on postsurgical, anesthetized monkeys have noted a relationship between fetal blood oxygen tension and the severity of FHR patterns. The accuracy of prediction of fetal outcome from FHR patterns which are defined as "normal" is 99% in expert hands. However, the "ominous" patterns are associated with poor fetal outcome in only 20-60% of cases. Such erroneous evaluation is undesirable, because it may precipitate obstetric intervention which carries its own risks. There is no study presently available which relates FHR patterns during labor to the adequacy of fetal oxygenation. We plan to begin investigating this in fetal lambs. Pregnant sheep will be prepared with catheters and flow probes several days before the studies. Measurements will be made of umbilical blood flow, fetal oxygen uptake, blood lactate and pyruvate, and uterine oxygen uptake. These factors will be related to features of the FHR baseline and periodic changes during spontaneous or induced labor under conditions of artificially produced impaired transplacental exchange. This study will define the degrees of hypoxia and dependence on anaerobic metabolism associated with the appearance of "ominous" FHR patterns, the ultimate goal being to assist in increasing the accuracy of predicting the compromised fetus.